IP Multimedia (IPMM) services provide a dynamic combination of voice, video, messaging, data, etc. within the same session. By growing the numbers of basic applications and the media which it is possible to combine, the number of services offered to the end users will grow, and the inter-personal communication experience will be enriched. This will lead to a new generation of personalised, rich multimedia communication services, including so-called “combinational IP Multimedia” services which are considered in more detail below.
IP Multimedia Subsystem (IMS) is the technology defined by the Third Generation Partnership Project (3GPP) to provide IP Multimedia services over 3G mobile communication networks. IMS sits on top of an access network which would typically be a General Packet Radio Service (GPRS) network but which might use some alternative technology, e.g. WiFi. FIG. 1 illustrates schematically how the IMS fits into the mobile network architecture in the case of a GPRS access network.
IMS provides key features to enrich the end-user person-to-person communication experience through the Integration and interaction of services. IMS allows new rich person-to-person (client-to-client) as well as person-to-content (client-to-server) communications over an IP-based network. So-called Serving Call Session Control Function (S-CSCF) nodes within the IMS are responsible for setting up and controlling calls and sessions between user terminals (or user terminals and web servers) using Session Initiation Protocol (SIP) and Session Delivery Protocol (SDP). The S-CSCF communicates with SIP application servers (ASs) which are responsible for authorising service use.
An example of a combinational IP Multimedia service is a multimedia service that includes and combines both a Circuit Switched media (such as voice) and a Packet Switched media over the IP Multimedia domain (such as pictures, video, presence, instant messages, etc.). A service referred to here as “WeShare” combines the full IP Multimedia Subsystem (IMS) benefits of a multimedia service with CS voice. The service enables a user, during a Circuit Switched (CS) voice conversation with another user, to take a picture, a video or audio clip, etc. and to share this content with other users in (near) real time. Either party in the conversation may initiate transmission of content to the other party.
The WeShare service may be the only IMS service an operator wants to allow in its network even though some user terminals may have general SIP technology installed (an operator may even want to restrict the WeShare service to the WeShare Image service in which users are only able to exchange still photos during a CS voice call). Furthermore, network operators may want to register subscribers on a per service basis. However, if a terminal has a SIP Client, and if the user has an IMS subscription, then today there is nothing preventing that SIP Client from setting up a SIP session requesting audio, video and/or data (effectively bypassing the WeShare SIP AS), even if the operator does not want these kind of general sessions to be created and/or the subscriber has not registered for the necessary services. This problem applies also to combinational services other than WeShare and indeed to non-combinational SIP-based services.